The United States has invited Myanmar to the world's largest multi-national military field exercise, a powerful symbolic gesture toward a military with a grim human rights record and a milestone in its rapprochement with the West.

Myanmar was invited to observe Cobra Gold, which brings together thousands of American and Thai military personnel and participants from other Asian countries for joint annual maneuvers, officials from countries participating in the exercises told Reuters on Friday.

"It's a significant and symbolic gesture that shows the rapprochement is gathering momentum," said Christopher Roberts, a security expert at Australia National University.

The invitation is part of a carefully calibrated re-engagement with Myanmar's military under the umbrella of humanitarian dialogue, the sources said, constituting one of the boldest rewards for Myanmar's new semi-civilian government after 49 years of direct military rule.

It is also seen as a first step towards US-Myanmar military-to-military ties, cut off after 1988 when soldiers opened fire on pro-democracy protesters in a crackdown that killed or wounded thousands and led to the house arrest of democracy champion Aung San Suu Kyi.

The invitation came after intense lobbying by Thailand, co-host of the exercises, the sources said.

It could prompt charges that Washington is moving too quickly in seeking to rehabilitate a military accused of continued human rights violations in ethnic regions such as Kachin State where tens of thousands of people have been displaced in 16 months of fighting.

"Burma's military continues to commit war crimes and crimes against humanity. It is shocking that the United States would invite them to military exercises," said Mark Farmaner, director of advocacy group Burma Campaign UK.

The invitation follows a visit this week by a delegation led by Michael Posner, the US State Department's top human rights official, to Naypyitaw, the capital of Myanmar, also known as Burma.

The US team also included Vikram Singh, the deputy assistant secretary of the US Defense Department, and other US military officials.

The talks on the Myanmar side were led by Aung Thaw, deputy minister for defence commodore .

Myanmar state media reported that the "two sides held talks on levels and operations of defence institutions of Myanmar and US and exchanged views on future dialogue and bilateral cooperation".

US officials in Bangkok and Washington declined to comment.

The invitation is another illustration of the Obama administration's pivot this year from Iraq and Afghanistan to focus national security resources on the Asia-Pacific region.

Military presence

Cobra Gold, which began in 1980, take places in Chon Buri, a province east of Bangkok where the United States built up a massive military presence during the Vietnam War.

Last year, about 10,000 US military personnel took part, along with about 3,400 Thais.

Five other countries participated - Indonesia, Japan, Malaysia, Singapore and South Korea. And nine countries sent observers, including China.

"In the past, Myanmar has always been unhappy about this Cobra Gold, thinking that it was directed against them and was like a step towards invasion," said Dr Tin Maung Maung Than, a senior fellow at the Institute of Southeast Asian Studies in Singapore and expert on Myanmar's military.

Even when it was a dictatorship, Myanmar sent more officers to the United States than to any other country.

More than 1,200 officers trained there between Myanmar's independence from Britain in 1948 and General Ne Win's military coup in 1962, according to Maung Aung Myoe, author of "Building the Tatmadaw: Myanmar Armed Forces since 1948".

Ne Win's coup ushered in nearly half a century of isolation and misrule, but the United States maintained military ties as a bulwark against the spread of communism from neighbouring China.

Some 255 Myanmar officers graduated from the US from 1980 to 1988 under the International Military Education and Training programme, more than from any other country, said Maung Aung Myoe.

The programme was halted, and US sanctions were imposed, after the junta crushed the 1988 uprising and refused to honour the results of a general election won by Suu Kyi's party two years later.